Introduction; Layer 3 Switching - D-Link DGS-3308TG User Manual

8-port Gigabit Ethernet Switch User's Guide
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I
NTRODUCTION
This section describes the Layer 3 functionality and Layer 2 and Layer 3 features of the DGS-3308 Series switches. Some
background information about Ethernet/Fast Ethernet, Gigabit Ethernet, and switching technology is presented. This is
intended for readers who may not be familiar with the concepts of layered switching and routing but is not intended to be a
complete or in-depth discussion.
For a more detailed discussion of the functionality of the DGS-3308, please see Chapter 5, "Switch Management and
Operating Concepts."

Layer 3 Switching

Layer 3 switching is the integration of two proven technologies: switching and routing. In fact, Layer 3 switches are running
the same routing routines and protocols as traditional routers. The main difference between traditional routing and Layer
3 switching is the addition of a group of Layer 2 switching domains and the execution of routing routines for most packets
via an ASIC – in hardware instead of software.
Where a traditional router would have one, or at best a few, Fast Ethernet ports, the DGS-3308 Layer 3 switch has eight
Gigabit Ethernet ports, including two which are GBIC-based. Where a traditional router would have one or two high-speed
serial WAN connections, the DGS-3308 relies upon Gigabit Ethernet ports to connect to a separate device, which in turn,
connects the network to a WAN or the Internet.
The DGS-3308 can be thought of as Fast Ethernet Layer 2 switching domains with a wire-speed router between each
domain. It can be deployed in a network between a traditional router and the intranetwork. The traditional router and its
associated WAN interface would then handle routing between the intranetwork and the WAN (the Internet, for example)
while the Layer 3 switch would handle routing within the LAN (between the Fast Ethernet Layer 2 domains). Any
installed Layer 2 switches, and indeed the entire subnetting scheme, would remain in place.
The DGS-3308FG can also replace key traditional routers for data centers and server farms, routing between these
locations and the rest of the network, and providing eight ports of Layer 2 switching performance combined with wire-speed
routing.
Backbone routers can also be replaced with DGS-3208FG and DGS-3208TG switches and a series of DGS-3308 switches
could be linked via the Gigabit Ethernet ports. Routers that service WAN connections would remain in place, but would
now be removed from the backbone and connected to the DGS-3308 via a Gigabit Ethernet port. The backbone itself could
be migrated to Gigabit Ethernet, or faster technologies as they become available.
Policy services can then be introduced (or enhanced) in the backbone infrastructure and maintained throughout the
network – even to the desktop. With a distributed infrastructure and a logical management structure, network
performance becomes easier to measure and fine-tune.
With the completion of the migration of the backbone to Gigabit or higher-performance technologies, the result is
inherently scalable and easily evolved for future technologies. This core network will also become the termination point for
Virtual Private Networks (VPNs) for remote office access to the enterprise infrastructure.
The DGS-3308 can then be thought of as accomplishing two objectives. First as a tool to provide high-performance access to
enterprise data servers and infrastructure, and second, to enhance the performance of network equipment already
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